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<DIV><FONT face=Arial size=2><SPAN
class=886414705-02012008>Dean,</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=886414705-02012008></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=886414705-02012008>I will give the site
a thorough read and get back to you, thank you for posting.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=886414705-02012008></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=886414705-02012008>To fill in some
detail as I have run a number of expirements already and have verified a few
data sets against google earth... I agree completely on the need for
more satellites in view. ProtoBot throws away all data until at
least 6 satellites are in view. The data always tracks, meaning that the
data points reported do not hop around, but rather follow transitionary
paths. Often the reported point will stay with-in a few feet boundary of
its last reported position for 15 or 20 minutes at a time, however, afterwards
it may up and track away 100 or more feet in a matter of a minute or less.
Often the reported position will return too within ~20ft of where it should be
(google earth reporting) inside of ~5 minutes.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=886414705-02012008></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=886414705-02012008>The screen snap shot
(sorry for the poor picture) was taken after ~20minutes of data capture showing
a 102 ft by 88 ft wandering path when the unit was stationary. I
have captured much longer paths that look similar, however my camera has
significant difficulty capturing this display w/wo flash other other
settings...</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=886414705-02012008></SPAN></FONT> </DIV><FONT face=Arial size=2><A
href="http://nikita.argia.net/kmaxon/sat_wand.jpg">http://nikita.argia.net/kmaxon/sat_wand.jpg</A></FONT>
<DIV><FONT face=Arial size=2><SPAN
class=886414705-02012008></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=886414705-02012008>I am most definitely
not an expert in the realm of GPS and those that I do know who are, work in
another division that precludes them from talking with to me.
Sigh... So close and yet so far...</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=886414705-02012008></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=886414705-02012008>-Kenneth</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> Dean Hall
[mailto:dwhall256@gmail.com]<BR><B>Sent:</B> Tuesday, January 01, 2008 11:35
PM<BR><B>To:</B> dprglist@dprg.org<BR><B>Cc:</B> Kenneth
Maxon<BR><B>Subject:</B> Re: [DPRG] Further Quandries on
GPS...<BR><BR></FONT></DIV>There are plenty variables about your GPS that I
don't know about so I could speculate plenty and that's all it would be. Here is
information on experiments I have performed:
<DIV><A
href="http://deanandara.com/Argonaut/Sensors/Gps/">http://deanandara.com/Argonaut/Sensors/Gps/</A></DIV>
<DIV><BR class=webkit-block-placeholder></DIV>
<DIV>Notably, coordinates can be off by as much as 120 meters just after module
power-up or when in view of only 5 or 6 sats. The SiRFstarIII that is in my GPS
module will give coordinates with increasing accuracy after taking multiple
readings; a.k.a. after time elapses. Multipath effects are not going to be
something you can measure (unless you have fancy equipment I don't know about;
which, if you did, you probably wouldn't be speculating like this), so start
with what you can measure. I suggest letting your receiver sit in one place for
a minute or five and examine the behavior of the coordinates: are they erratic
or are they converging? If they are erratic, try again a different location
& time. If they are converging, find out more information, like how many
sats in view? and how long until the coordinates are within 3 meters of actual
(I use Google Earth for that)?</DIV>
<DIV><BR class=webkit-block-placeholder></DIV>
<DIV>By running little experiments like this, I know that my robot warm-up
procedure will include turning on the GPS module and waiting until a significant
number of sats have been in view for an amount of time that I determine. Only
then will I start trusting my GPS coordinate values. I have written a few Python
scripts that help me capture, convert and view data from my GPS module. For
example, just reading NMEA sentences with the receiver at one location for 5
minutes, save the data, convert to a KML file, plot it as a path and view it
using Google Earth. This helps visualize where your receiver thinks it is.
Scripts are here:</DIV>
<DIV><A
href="http://deanandara.com/Argonaut/Sensors/Gps/Scripts.html">http://deanandara.com/Argonaut/Sensors/Gps/Scripts.html</A></DIV>
<DIV><BR class=webkit-block-placeholder></DIV>
<DIV>!!Dean</DIV>
<DIV><BR class=webkit-block-placeholder></DIV>
<DIV><BR>
<DIV>
<DIV>On Jan 1, 2008, at 21:18 , Kenneth Maxon wrote:</DIV><BR
class=Apple-interchange-newline>
<BLOCKQUOTE type="cite"><FONT id=role_document>
<DIV></DIV>
<DIV><SPAN class=124190303-02012008>Hello DPRG...</SPAN></DIV>
<DIV></DIV>
<DIV><SPAN class=124190303-02012008>Here is one for further conversation in
the "Hmmm...?" realm...</SPAN></DIV>
<DIV><SPAN class=124190303-02012008></SPAN></DIV>
<DIV><SPAN class=124190303-02012008>It was up to a fair 8-deg today and
although there is a significant snow pack on the ground the sun was bright and
the sky was clear for a few hours so ProtoBot ventured back out into the back
yard for more GPS expiremental data gathering.</SPAN></DIV>
<DIV><SPAN class=124190303-02012008></SPAN></DIV>
<DIV><SPAN class=124190303-02012008>This time I made sure that ProtoBot was a
full 12 ft away from the house and this time, the house does not have a
1/2"~3/4" glaze of ice hanging on it. There is however a 3/4" layer of solid
ice under the snow back that ProtoBot is sitting on. I pulled a bonehead move
and forgot to take my hand held Garmin + adapter & extension cord out to
verify the readings, however, surprisingly ProtoBot still recorded erronous
readings, like it was doing inside and in the previous outdoor trial up along
side the house.</SPAN></DIV>
<DIV><SPAN class=124190303-02012008></SPAN></DIV>
<DIV><SPAN class=124190303-02012008>I have taken time to swap out the GPS
module / antenna combination on ProtoBot with the spare unit that I'll be
using on an upcoming project. And given that ProtoBot's last round of testing
performed in a similar (although less drastic from an error standpoint) manner
than did the comercial Garmin unit, I still have a quandry here. Yes, I am
still wondering *IF* this could be coming from multipath off of the ice layer.
I theroise that it is not as the 10" of snow pack sitting on top of the ice
should be enough to completely disburse the energy, and all of the sattelites
reported by the module as being used in the actual position calculation had a
good signal strength reading.</SPAN></DIV>
<DIV><SPAN class=124190303-02012008></SPAN></DIV>
<DIV><SPAN class=124190303-02012008>I don't know that anyone on this list will
have input, however it is an interesting quandry that I am working through and
I thought it might be of interest to the group, as there are others in this
group that activly use GPS on their robots.</SPAN></DIV>
<DIV><SPAN class=124190303-02012008></SPAN></DIV>
<DIV><SPAN class=124190303-02012008>Of course I'll post futher when I get to
the bottom of the issue... </SPAN><SPAN
class=124190303-02012008>-Kenneth</SPAN></DIV>
<DIV><SPAN class=124190303-02012008></SPAN></DIV></FONT>
<DIV><FONT id=role_document><SPAN class=124190303-02012008>BTW, Ron, the
package arrived, thank you. You didn't have to return it but since you did
I'll put it to good use in the next project. (IE, you've saved me from some
eBay surfing). -Thanks...</SPAN></FONT></DIV>
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